Solid core ceramic matrix composite articles find their use in turbine components as well as other applications. Combustion turbines are well known in the art as having a compressor section for supplying a flow of compressed combustion air, a combustor section for burning a fuel in the compressed combustion air, and a turbine section for extracting thermal energy from the combustion air and converting that energy into mechanical energy in the form of a shaft rotation. Many parts of the combustor section and turbine section are exposed directly to the hot combustion gasses, for example the combustor, the transition duct between the combustor and the turbine section, and the turbine stationary vanes, rotating blades and surrounding ring segments.
A construction of a ceramic matrix composite (CMC) shell and solid ceramic core has been proposed for use as a turbine vane airfoil for one or more beneficial reasons. In one aspect, these articles include a solid core and the solid core is effective at reducing pressure loads caused by the high pressure cooling air on the inside of the airfoil. In another aspect, these articles may include channels cast within the core, thereby permitting a cooling air flow to be directed through the channels. Another potential benefit of using these articles is to increase robustness of the airfoil construction—a solid core provides bending rigidity and strength, increases impact resistance, and resistance to cyclic excitation (HCF).
While these CMC shell and solid ceramic core articles offer the potential for higher operating temperatures than do metal alloy materials due to the inherent nature of ceramic materials, as well as one or more of the previous benefits, CMC materials generally are not as strong as metal, and therefore the required cross-section for a particular application may be relatively thick.
Temperatures in excess of 1600° C. may be problematic with solid core CMC airfoils, wherein the different ceramic materials that make up the airfoil may have different properties, resulting in internal strain within the core. This mismatch results in stress at the interfaces of the multilayer system and often results in poor bond strength and/or delaminations.
Prior art methods of making airfoils and other ceramic articles fail to address these issues regarding delaminations and/or internal strains that may occur within these airfoils.
Accordingly what is needed is a method of forming ceramic matrix composite shell/solid core articles that alleviates the problems of prior art methods of forming these articles. Also what is needed is a solid core ceramic matrix article that is more resistant to internal strain. Also what is needed is a method that is effective at forming solid core ceramic matrix composite articles in a cost-effective and/or efficient manner.